The invention described herein pertains to a method and apparatus for improving the economics of production from a producing well. While the descriptions of the invention contained herein are given with respect to producing gas wells, it will be understood by those of skill in the art that they are also applicable to producing oil wells for the reduction of lifting costs therein.
A problem associated with the production of oil and gas throughout the history of the industry has been that of the disposal of undesired water produced along with the desired oil or gas. The above referenced co-pending application deals with the re-injection of produced water into an injection zone lower in the producing well. The produced water is separated by using the casing-production tubing annulus as a gravity separator in the wellbore in a producing oil well. The oil is pumped to the surface and the produced water is pumped into a set of injection perforations lower in the wellbore, and sealed off interior to the casing from the producing perforations by a production packer. This packer is penetrated by a tubing string connected to a dual action mechanical pump located above the packer which pumps oil to the surface on the upstroke of the pump, and which pumps water into the injection perforations below the packer on the downstroke of the pump.
The pumping system described in the referenced co-pending application has been in operation a sufficient time to permit observation of some weaknesses in the system. One such weakness, which the present invention addresses, is that of the valving used to selectively pick up the water or oil for pumping to the injection perforations or to the surface respectively. The valves used in the referenced application had relatively small cross sectional area, necessitating the use of a plurality of such valves. This can lead to earlier failure because of a multiplicity of parts. Also the valves previously used were of a spring loaded or biased type, which used spring pressure to assist in the opening and closing of valves. The use of springs in the high temperature, often corrosive, well fluid environment would be better avoided, if possible. The present invention does so by completely eliminating the use of spring operated or assisted valves.
Typically gas wells flow to the surface using the reservoir pressure as a means of lifting the gas which is produced into the cased well borehole through production perforations and is allowed to enter a production tubing string run coaxially into the casing and extending from the surface down to the producing zone. Over time, essentially all gas producing wells also produce unwanted water along with the gas into the casing. This builds up a hydrostatic pressure head in the casing-tubing annulus which must be overcome by the formation pressure, or by a pumping system, to produce gas and fluid to the surface through the tubing string or the casing-tubing annulus.
The production of salt water creates a water handling problem. The water is conventionally separated at the surface in gravity or other type separators and is then re-injected into a disposal well or hauled off by truck to be disposed of. A typical way of reducing the undesired hydrostatic head problem, which slows gas production, is to pump the water to the surface and to allow gas to flow to the surface in the tubing-casing annulus. Again, this creates a water disposal problem. The reinjection of water downhole in a manner similar to that disclosed in the above referenced patent application can significantly reduce lifting costs and can virtually eliminate waste water disposal problems.